add this facility

    i74 : for i from 4 to 0 by -1 do nothing
    stdio:75:17:(3): error: no method for adjacent objects:
    --            0 (of class ZZ)
    --    SPACE   by (of class Symbol)

and this

    i78 : QQ[x,y]

    o78 = QQ[x, y]

    o78 : PolynomialRing

    i79 : for i from x to x+10*y by y do print
    stdio:80:12:(3): error: expected an integer

and parallel "for"


